BORO have been left walking a central defensive tightrope after Stephen McManus was ruled out for four months.

The Scots stopper has been sidelined after ankle ligament surgery in a specialist London hospital yesterday.

The commanding McManus picked up the injury as he crunched into a tackle early in Boro’s 2-1 home win over Crystal Palace before limping off six minutes before the break.

He had played every minute of the season before that.

The former Celtic man had two bones drilled and fused in his ankle and the ligaments secured during surgery and, while a full recovery is expected, he will be out of action until the middle of March.

“It’s obviously a big blow for Stephen but also for the team because he is a strong, experienced defender and a leader too,” said Boro manager Tony Mowbray.

“He is going to be missed. We wish him all the best in his recovery and rehab.”

However the Boro boss insisted the blow gave a chance for others to secure a shirt.

“Every injury creates an opportunity for others to press their claims and this one is no different, from that point of view,” he said.

“The back four have performed exceptionally well over the last couple of games. They have stepped up to the mark since Stephen’s injury but they have to keep that going.”

The news leaves Mowbray with a massive headache, though. With just three central defenders fit and available he is just one injury or suspension away from a crisis.

The defensive crisis will also sharpen the boss’s thinking as the transfer window looms.

Redcar Rock David Wheater has been in fine form but he is on four yellow cards and just one booking from a ban.

Matthew Bates - Wheater’s long term partner going back to the 2004 FA Youth Cup win - has slotted into the gap left by McManus at the back and has impressed.

Beyond that, however, there is little experience to call on.

Seb Hines, 22, has been on the bench several times this season but since making a goal- scoring debut in an FA Cup third round win over Hull in January 2007 he has made five senior starts and come off the bench four times. He has impressed in his rare outings but has a chequered injury record.

Of Boro’s other central defenders Jonathan Grounds is out on loan at Hibernian and cannot be recalled until January.

Aussie Rhys Williams has excelled in central defence for the reserves and in odd cameos in the first team but is out with a pelvic muscle injury that will sideline him for at least another month.

On-loan Matthew Kilgallon, who was blooded at Boro at left-back under Gordon Strachan but in reality is an experienced centre-back, is currently with parent club Sunderland getting treatment for an ongoing back injury.

BORO take on Hartlepool in a reserve team fixture at Billingham Town tonight (7pm).